This invention relates to an automatic pressure control apparatus for a counterbalancer fitted to a press.
A conventional press is provided with a counterbalancer for supporting the weight of slides, cranks, connecting rods, punches or upper dies so as to enable smooth upward and downward movements of the slides. Regarding the counterbalancer, it is necessary to vary its supporting force depending on the weight of the upper die to be fitted to the slide. For this reason, there have heretofore been suggested various kinds of automatic control apparatus for counterbalancers wherein the weight to be supported by the counterbalancer can be automatically adjusted depending on the weight of the upper die. One of such embodiments is disclosed in the Japanese Utility Model Publication No. 21813/1978. According to the invention of this Utility Model, the arrangement is made such that, each time when the weight of the upper die to be fitted to the slide varies, a stop valve located between an air reservoir and a pressure supply source is shut off and, at the same time, a manually operable stop valve is opened so as to lower the pressure within the air reservoir communicating with a balance cylinder to the level of the balancing pressure which is obtainable when the upper slide is not fitted to the slide thereby adjusting the height of the slide, and thereafter the stop valve on the side of the pressure supply source is opened, and simultaneously the manually operable stop valve on the pressure release side is shut off, and subsequently, a reducing valve is manually adjusted while observing the pressure inside the air reservoir by means of its pressure gauge so that the pressure in the pressure chamber of the balance cylinder can be set at a value necessary for suspending the upper die.
However, the apparatus described in the aforementioned Utility Model Publication is disadvantageous in that the manual adjustments of the balance pressure require troublesome operations and tend to cause adjustment errors.